The problems is, I'm not sure if 後で fits here.
I feel that the で in 後で is very intentional-verb-like.
Is it suitable to use it to express a condition?
I don't know.

If you use で here, I might interpret it as “急いで帰った後でビールを飲む、そういう場合が多い”. 後で introduces essential information.(or new information, or restrictive clauses? I'm not sure what's the proper term to be used. It tells you “when to drink”, used as a “normal adverbial when”)

In your sentence, the 後 is used more like a conjunction, which relate the existing, or known situation(急いで帰った) with a new situation(ビールを飲む). It's more “relative-pronoun-like”.
I don't know if in English you can say something like “I hurry home, after-when I drink beer.” or not. You may simply take it as “, and then”.

You can find a lot of examples by searching そのあと・その後 in the website you provide.
(It says there is a “where-after”, but it doesn't say anything about “after-when” or “when-after” )

More over, it's also condition-like, so は might be added here.

My feeling might be completely wrong, because I'm puzzled by usage of 格助詞・は・無助詞, too.
I hope a native speaker will confirm it.

I would say,
'When I approach it with flat awareness, then often I feel good about it
when I listen to it later."

That's what I wanted to know! So still, can be used the word 'listen',
that's why when the native japanese translate it as:

" .....it works when he creates his music with ‘flat mind"
I asked myself "why the word 'to listen' was cut off in the translation"?

Actually , the word 'listen' is still there. I don't like to change totally the original sentence, so it was strange to me, because still, it make sense to me to keep the word 'listen' in the english translation too.

That's was the translation I'm talking about :

tokyotower wrote:
FLAT意識で臨んだ時の方が後で聴くといいかんじの場合がおおい。
(there's good feelings when you listening to it later with
flat mind ('relaxed mind')

quote:No. He says that it works when he creates his music with ‘flat mind’ (in
a straightforward manner, I guess).

------------------

Both translations are correct of course, but I prefer this translation, because it still keep the words like in the original sentence:

FLAT意識で臨んだ時の方が後で聴くといいかんじの場合がおおい。I would say,
'When I approach it with flat awareness, then often I feel good about it when I listen to it later."

Tokyotower, I just pointed out your mistake. I did not “translate” that for you.
There is a big difference between “compose with flat mind” and “listen to it with flat mind”. All that the writer wanted to convey is:

Compose with "flat mind" → Works (in many cases)
Compose without "flat mind" → Doesn’t work

Don’t try to literally translate when you don’t know the grammar very well. Instead, try to understand what the writer wants to tell you. That’s my advice for you.